Clown

The analogy of stickmen living on 2D paper universes is also useful with the concept of curved spaces.

Spacetime does not owe it's existence to matter in the sense of particles, atoms, etc. GR can describe universes where no matter exists at all, but this still doesn't leave room for independent existence of space, because the gravitational field still exists. The motion of an object will at the very least, be in relation to the field. The empty space in between galaxies is expanding.

Wow, cranky.

I think there should be a theory development forum here.

It has wonderful pictures. Some of these artists working on images for physics books (and CNN's space website) can make a mediocre book worthwhile. But maybe I just like that kind of art more than most folks.

Does what because everything moves?

Yes, Homer Simpson's hyperdounut. It's one possible multiply connected shape for the universe, while a hypersphere would be simply connected.

The universe is not expanding into a vacuum or any medium. The flat space in between galaxies itself expands, and there is no need for an embedding space.

Sounds like the block universe.

He's right, don't. Anyway, I think it's easier to just say the universe is infinite and that's why there's no edge or center. It's much easier than trying to explain Non-Euclidean geometry with clumsy balloon analogies.

In the normal rules of euclidean geometry, it would seem you would find a center of a finite universe. But remember that we aren't dealing with Euclidean geometry - we are dealing with the curved spacetime of general relativity. Without learning Non Euclidean geometry, you can use the analogy of any curved 2D surface to see how the universe could be without a center. Often, surfaces such as that of tables are flat, but they can also be curved as in the case of a balloon. In that case, at no X,Y point will you be able to find a center. The analogy has its shortcomings, mainly because the universe is not the curved area of a surface, it's a curved volume. Furthermore, the term "fabric of spacetime" is somewhat of a popular physics word that isn't meant to be taken too literally. Spacetime isn't considered to be an aether like medium, and there is no actual substance that empty space is consisted of. Following from that, the universe should be in no danger of tearing from the expansion.

I'll second that. WC2 has a good thing going, and I would have liked to see a WC3 built on that with additional units, updated graphics and new features. This new style with the RPG element ruined it for me.

Very true. Whenever a sucessful theory is replaced by something better, the new theory is usually an improvement on the old. It's never a case of throwing away the old completely.

In the case of the expanding universe, we'd need a new model that can explain the evidence as well as GR can.

There's also really no quantum theory of spacetime, so the classic model of the expanding universe is all we have to explain the data. As of now, the big bang is purely a classic theory.

No, it's not conjecture. The expanding universe model is predicted by general relativity. The big bang is based on GR, and when you run back the clock on the universe you find a much smaller volume of space. The expanding universe does not need to embedded in any larger space.

The big bang wasn't an explosion into empty space. The term big bang is not the best, and is misleading. A better to think of it is that the space itself starts to expand, not matter moving into some pre existing static void.

You only get that problem if you insist on starting with state before the big bang in the first place. Often though, the claim is that there is no before or prior state at all, meaning no cause needed.

For an introduction with no math, anything on the subject by John Gribbon. Also, if you're looking for info about a unified field theory (theory of everything) you might want to grab a copy of Hyperspace, authored by Michio Kaku. It's an easy to read book, and explains the importance of geometry in the search for a quantum theory of gravity. A search on Amazon should turn up some results.

Whut is a What.

No, but I don't think he did either. Any scientific proposal for the universe coming into existence as a vacuum fluctation will require the laws of physics to exist first. But as I said, physicists can be confusing at times, and many interpret some quantum nothing state to be the philosophical concept of nothingness. So this confusion causes many to make the all common fallacy of reification of the zero, even though it's not based on any physics.

Fair enough. Back to cosmology then.....

Physicists are often just sloppy with the english language. The absolute nothing they sometimes call a void is supposed to be a quantum state where spacetime does not yet exist. Still, they call it nothing. It gets worse, because some still call the vacuum nothing as well, causing all sorts of confusion. It's similar to the confusion that comes from the use of the word "observer" in quantum mechanics.

Indeed, but those theories all require that the laws of physics exist even when space and time didn't. To many physicists, the idea that some arbitrary laws of physics have existence independent of the actual fields they govern, is rather silly. But hey, that's a whole new can of worms. But then, you could just easily say there is literally no "before" the big bang at all, in the same way that there is no "outside" of space.

I think you covered that above.